you need to go back to the

#170291
Avatarpaulears
Participant

you need to go back to the history – interlaced scan exploited the phosphor persistence problem by illuminating one field, then then next – so the phosphors were excited and blurred the swap from one frame to the next – the fact each was only half the maximum resolution didn’t matter too much. As technology got better, they were able to refresh the fields quicker – usually double the rate and this cut down flicker even more. The snag with this interlaced system is that anything that moves between frames tends to twitch between the two fields. Film exposes a complete frame at a time, progressive scan is very similar.

So your question on the disappearing field is quite right – on a crt, the old image fades away, while the new one is being built – a kind of very fast crossfade, hiding the join. So although we talk of 30fps, we’re talking 60 half resolution frames per second, really. So shooting at full format progressive is similar to slowing the shutter speed – much more care has to be taken with movement – shakes and vibration are a major problem, and you have to modify your shooting technique.

When TV technology really took off, here in the UK we did a have a few issues with picture quality – our 25fps/50 fields system found fast motion difficult to reproduce. Watching Formula 1 on a modern set with greater resoloution, and less phosphor persistence enabled the snags with hih shutter speed cameras to be seen. The camera technology had got a lot better and high shutter speeds were available that really sharpened up moving images – the problem being the tv’s couldn’t cope!

I’m not sure that really answered the question – did it?

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